Anyone can explain why light passes through the object?
Select your light, and under Properties, check the box that says &quot;Contact Shadows&quot;.

As you can see, however, a small amount of light still bleeds through. If this happens, it can usually be eliminated by giving your object more thickness. In the example below, I used a solidify modifier to make it thicker.

It seems like the only problem areas in your object are concerning the &quot;bands&quot;. Make sure they have both inside and outside faces, and that they are correctly aligned with the rest of the mesh.
Lastly, though I cannot tell from your photo, it looks like your object may be mirrored on the Z axis. If this is the case, make sure the two halves merged correctly, and if you're using a modifier to achieve this make sure &quot;Clipping&quot; and &quot;Merge&quot; are enabled.